1. Field of the Invention
The present invention relates to an appearance inspection apparatus and an appearance inspection method and, in particular, to an appearance inspection apparatus and an appearance inspection method for detecting the shape, surface unevenness, and changes in color tone of a sample under inspection, such as a tire or a tire component.
2. Description of the Related Art
Tire appearance inspections conducted conventionally are shape inspections and surface condition inspections of tires. In a shape inspection, a monochromatic slit light is cast in a radial direction on the surface of a rotating tire and the portion illuminated by the slit light is captured by an area camera. By doing so, sectional images for one rotation of a tire are acquired. Then the thus acquired sectional images are subjected to an image processing and compared with a master image to determine whether there is any shape anomaly or not. Also, in a surface condition inspection, attempts are made to detect minute surface unevenness that cannot be detected in a shape inspection. To do so, red illumination and blue illumination having different wavelengths from each other are directed to the surface of a rotating tire from different directions so as to overlap the cast lights with each other. Then the surface images for one rotation of the tire are acquired by capturing the portion illuminated by the overlapped lights by a line camera all along the circumference of the tire. Then the red component and the blue component contained in the surface images are separated from each other, and the presence or absence of unevenness of the tire surface is determined from the ratio between the intensities of the red component and the blue component. Also, the inclination angles of the tire surface are calculated based on the intensities of the red component and the blue component, and the surface condition is inspected by evaluating the agreement between the changes in the inclination angle distribution and the defect characteristics (e.g., a decision on no anomaly when the inclination angle is at or below a threshold and on surface unevenness anomaly when it is greater than the threshold).